1. Field of Technology
This invention relates to an optical recording head and an optical recording apparatus.
2. Description of Related Art
In recent years, higher density of an information recording medium is required and recording methods of various types have been proposed. A thermally assisted magnetic recording method is also one of them. Since it is necessary to make the size of each magnetic domain smaller to achieve higher density, a material having a large coercive force is utilized to store data stably. In such a recording medium generation of strong magnetic field is necessary at the time of writing, and there are limitations to a small head corresponding to a domain having been made smaller.
Therefore, proposed has been a method to assure the stability of recorded magnetic bits by causing magnetic softening by local heating at the time of recording and recording is performed in a state of decreased coercive force followed by stop of heating to allow natural cooling. This method is called as a thermally assisted magnetic recording method.
In thermally assisted recording method, it is desirable to perform instantaneous heating of a recording medium. Further, contact between a mechanism of heating and a recording medium is not allowed. Therefore, heating is generally performed utilizing absorption of light, and a method to utilize light for heating is called an optically assisted method. In the case of performing high density recording by an optically assisted method, required is an optical spot as minute as not more than the wavelength of utilizing light.
Therefore, employed is an optical head which employs near-field light (also referred to as light of near field vision) emitted through an optical opening having a size of not larger than the wavelength of incident light. The followings have been proposed as an optical recording head having an optical spot as minute as described above (Refer to U.S. Pat. No. 6,944,112)
An optical recording head is equipped with a writing magnetic pole, and a wave guide provided with a core layer and a clad layer which are adjacent to said writing magnetic pole. A core layer is provided with a diffraction grating to introduce light into said core layer, and such as parallel laser light is efficiently coupled with the core layer when laser light is irradiated against this diffraction grating at a predetermined incident angle. Light coupled with a core layer is converged to a focal point located in the neighborhood of the top portion of a core layer and a recording medium is irradiated and heated by light radiated from the top portion, whereby writing is conducted by a writing magnetic pole.
The above-described element in which laser light is incident at a predetermined angle, being coupled with a wave guide and converged to be emitted from the top portion, is called as a wave guide type solid immersion mirror (PSIM: Planar Solid Immersion Mirror).
In PSIM utilized in an optical recording head, which is disclosed in U.S. Pat. No. 6,944,112, it is necessary to make laser light incident at a predetermined angle; however, a specific method to introduce light into PSIM (hereinafter, referred to as a wave guide) has not been disclosed.
To make light incident into a wave guide at a predetermined angle, a light source is necessary to be arranged obliquely above the wave guide; however, the thickness of an optical recording system becomes large when a light source is arranged in such a position.
Further, there is a case to utilize semiconductor laser light as light introduced into a wave guide. In a semiconductor laser such as a Fabry-Perot resonance type, a so-called mode hop phenomenon will be generated to vary the oscillation wavelength when there is a temperature variation. Since the diffraction angle is varied when a wavelength of light incident into the diffraction grating of a wave guide varies, efficiency of optical coupling with a wave guide will be decreased. To prevent decrease of the optical coupling efficiency, it is necessary to vary the incident angle into a diffraction grating of a wave guide depending on wavelength variation.
This invention has been made in view of the above-described problems and the object is to provide an optical recording head and an optical recording system which are provided with an optical element which has a simple constitution and can efficiently introduce light into a wave guide.